1. Field of the Invention
This application relates to a high-performance vertical metal oxide film semiconductor field effect transistor (MOSFET: Metal Oxide Semiconductor Field Effect Transistor) and its manufacturing method using a field effect transistor, especially a carbon nanotube as a conductive channel.
2. Description of the Related Art
Studies to shorten the gate length of a transistor are actively carried out than before. At present, the shortest gate length is 8 nm in a MOS structure transistor manufactured by electron beam exposure. However, for this transistor, there are problems of large dimensional fluctuation of the gate, inferior linearity and not practical. There is a limit to the microfabrication of a transistor by the top-down method based on such Si technology and the development of new microfabrication technology is strongly desired.
On the other hand, as a break through for the microfabrication of a transistor by the top-down method based on Si technology, forming a field effect transistor (FET) by the bottom-up method using a microfabric carbon tube is proposed. The concerned field effect transistor is an element converting an input voltage signal in a gate electrode to an output current signal from a source electrode or a drain electrode, and based on the difference of the structure, it is roughly divided into a horizontal field effect transistor where a current moves parallel to a substrate surface and a vertical field effect transistor where a current moves vertically to a substrate surface. Of these, in the case of the concerned vertical field effect transistor, one side of the main electrode is on the bottom side of the transistor element and excels in conducting ability per unit area in comparison with the horizontal field effect transistor, and according to the laminate thickness, the gate length is determined, therefore, there are advantages such as the controlling and microfabrication of the gate length at several nm level by layer laminated process is possible. Recently, vertical field effect transistor using carbon nanotube excelling in properties such as chemical stability, electric conductivity, electron emission ability, mechanical strength, or thermal conductivity in gate electrode and conductive channel is proposed (for example, Applied Physics Letters, vol. 79, p. 3696, 2001 and Japanese Patent Application Laid-Open (JP-A) No. 2002-110977). Specifically, as shown in FIGS. 1A to 1C, a vertical field effect transistor (FET) where multi-hole 65 is tessellated formed on insulating layer 60 comprising of alumina or silicon, carbon nanotube 20 is developed inside hole 65 in a vertical direction, drain electrode line 80 and source electrode line 90 are linked respectively to the upper part and lower part of the insulating layer 60 with the carbon nanotube 20, and gate electrode line 70 is provided in the upper part of the drain electrode line 80, is proposed.
However, in this case, the carbon nanotube used as the conductive channel is a multi-layer carbon nanotube of comparatively big diameter formed one tube by one tube inside the hole of the insulating layer, and for the concerned multi-layer carbon nanotube, the electrical property of each layer differs and materials that have metal property and materials that have semiconductive property mix together, therefore, there is a problem of not performing sufficiently the semiconductive controlling, that is, the channel current controlling by the gate electrode. The gate electrode controlling the current of the conductive channel is formed at a position apart from the carbon nanotube on the drain electrode, therefore, there are problems such as the distance between the gate electrode and the conductive channel (carbon nanotube) is big, the gate capacity necessary during modulating of channel current is not sufficient, and sufficient device performance can not be obtained.
A field effect transistor where the distance between the conductive channel (carbon nanotube) and the gate electrode is shortened is also proposed (for example, Japanese Patent Application Laid-Open (JP-A) No. 2003-109974). However, in this case, as the gate spacing and channel spacing are determined by patterning method, due to the fluctuation of the patterning, there are problems such as the gate spacing and channel spacing also fluctuate and the controlling of the channel current becomes insufficient.
Thus, the present situation is that a high-performance vertical field effect transistor where the distance between the gate electrode and conductive channel is small and capable of performing sufficiently channel current controlling by a gate, and a method effectively manufacturing the field effect transistor, are not yet provided.
Under these circumstances, the present invention has been accomplished, and the objects of the present invention are as follows. Specifically, an object of the present invention is to provide a high-performance vertical field effect transistor having a microminiaturized structure in which the distance between the gate and the channel is made short not through a microfabrication process, having a large gate capacitance, and so elaborated that the gate can control the channel current with a low voltage, and a method for simply and efficiently manufacturing such a field effect transistor not through a complex process such as a microfabrication process.